1. Field of the Invention
The invention pertains to a process for determining the dye uptake of polyethylene terephthalate fibres.
2. Description of the Related Art
A well-known, long-used method of determining the dye uptake of polyethylene terephthalate fibres is to employ a comparative test in which various fibre samples have their different uptakes of a standard dye determined. To this end small pieces of yam of different samples are knitted into a hose. Next, the hose is dyed with a dye critics to the material under critical conditions, i.e., the time during which the knitted hose is contacted with the liquid in which the dye is dissolved is too short to effect full saturation of the hose with dye or complete uptake of the dye from the bath. In addition, such a test employs dyes which have a slow uptake by the fibrous material in question, and the determination is carried out at a comparatively low temperature. The dye uptake is then evaluated visually by indicating whether a yam sample""s dye uptake is superior, inferior or normal as compared with that of the yam sample next to it. Major drawbacks of this known method are that:
the results obtained are relative
the determination is dependent on the person carrying out the test
the method is complex and time-/labour-intensive
only comparatively large differences in dye uptake can be made visible
Admittedly, it is possible to do away with the subjective elements present in this determination by using photometric equipment (e.g., a HunterLab spectrometer), but it was found that in that case the knitted structure of the hose has a major effect on the determination.
For that reason there is great need for a method of swiftly and simply determining the dye uptake of polyethylene terephthalate fibres in such a manner as will enable an absolute comparison among the fibre samples. The invention now provides a process by which this requirement is satisfied fully or for the most part.
The invention consists in that in order to determine their dye uptake, the polyethylene terephthalate fibres are irradiated with high-intensity monochromatic light and a light-sensitive sensor is used to measure the Raman scattering and compare it with that of an earlier established model on the basis of Raman spectra of polyethylene terephthalate fibres of known composition and structure, whereupon a model is used to calculate the density, which constitutes a quantitative measure of the dye uptake, use being made in the calculation of measurement points from a number of regions within the spectral measuring range of 598 to 1900 cmxe2x88x921, where out of a total number of measurement points of 100%:
a. 40-100% originates from the spectral region of category X,
b. 0-30% originates from the spectral region of category Y, and
c. 0-60% originates from the spectral region Q belonging to neither category X nor category Y,
xe2x80x83the spectral regions of the categories X and Y, respectively, being formed by:
and the measurement points from the spectral region of category X originating from at least six out of the eight sub-regions of category X.
The invention also pertains to polyester fibres selected for uniform dye uptake by means of the aforementioned process.